Meaning
What does I Second That mean?
I second that is a phrase used to express the approval of a proposition, opinion or idea.
It is originally a parliamentary phrase, adopted by most people in their everyday speech, turning it a common expression of support.
Origin
What's the origin of I Second That?
The expression “I second that” was adopted into English from the Middle French “seconder” in the end of the 16th century.
The first recorded case of the phrase used in a parliamentary sense is dated to 1597.
Spread & Usage
How did I Second That spread?
“I second that” was adopted into common speech during the 20th century, when mass media had become available for most people in the west, involving them into the process of democracy.
The expression was first defined on Urban Dictionary on August 2nd, 2005.

External resources
- Quora – What does “I second that” mean?